Many different kinds of additives are used in the manufacture of paper products. For example, in techniques for coating paper, cardboard or the like, coating compositions may be used that contain one or several inorganic fillers, one or several binders and various additives. The goal of coating is to improve certain physical and optical characteristics of paper, such as but not limited to, gloss, brightness, opacity, capability for ink printing, smoothness and other properties of great commercial importance.
A composition for coating paper is generally formed from a filler which may comprise one or several pigments, one or several polymer binders and various additives such as, especially, a lubricant such as calcium stearate, a wax emulsion, or a fatty acid ester, and possibly antifoaming agents, and the like, as is known in the art.
In another example, the paper manufacturing industry generally uses cellulose, mechanical wood pulp, or fillers, such as kaolin or chalk and rosin sizes, as the principal components for paper and carton stock. Papers often need “sizing”, i.e. hydrophobing. This is necessary in order to give writing paper proper ink resistance, to avoid “feathering”. Similarly, printing stock should give a clear print with the best possible reproduction of contrast and with the minimum demand for printing ink. Also, for semi-manufactured products, such as base-paper for coating purposes, a limited degree of sizing is required to limit the degree of penetration of size-press preparatory solutions or surface coatings; full sizing is not desirable in this case because, apart from economic considerations, it would lead to a repulsion or separation of the surface treating material. There is therefore a distinction between full and partial sizing, e.g. half, quarter or one-eighth sizing.
The strength properties of paper and paper products include, but are not limited to, burst, tear, tensile, fiber bonding, crush strength, chemical resistance (e.g., to water, salt, oil) and the like. For example, in the paper-making process, cellulosic fibers may be softened with water before being processed into paper. Fillers such as clay, titanium dioxide, talc, and calcium carbonate, are added to the papermaking process to improve paper properties such as opacity, brightness, and printability. Each filler is unique due to differences in physical-chemical and morphological properties. One example of a substance which will reduce linting or dusting is clay. Titanium dioxide is an excellent filler for opacity purposes due to is high refractive index and small particle size. Due to its hydrophobicity, talc is an excellent pitch/stickiness control. In addition, talc is an excellent filler for purposes of improving machine drainage, sheet smoothness and printability.
U.S. Pat. No. 1,792,382 to Lodge et al. teaches that “waxes and fats generally, and paraffin specifically, materially improve the water resistance of paper and paper products when incorporated into the sheet of paper either by the process commonly known as engine sizing in which process a solution, emulsion or finely divided dispersed suspension of wax or waxes alone or in combination with rosin and/or other ingredients, is added to the paper pulp in the beaters”. The wax suspension in Lodge et al. is a suspension of solid wax particles in a solvent.
European Patent EP0026091 describes a hydrophobic filler for papermaking, particularly in the production of partly to fully sized paper or carton stock. The hydrophobic filler is used in conjunction with a wax-based emulsion.
U.S. Pat. No. 6,565,646 to Lasmarias et al. describes a talc additive for use as a filler in making paper products which is useful in preventing dusting or Tinting of paper. The talc is milled to have a particle size of less than 10 micrometers and a cationic charge to the surface of the talc particles. For example, a cationic charge can be added to the particle by mixing talc particles with water to create a slurry and, adding a cationic compound to the slurry. In preferred embodiments, the cationic compound is selected from cationic wet-end starch, cationic wax-based emulsion, polydadmacs and carboxymethylcellulose.